THE DIASTOLIC FILLING OF THE HEART. 



47 



minutes, for the supply of oxygen is not exhausted, owing to the absence of 

 asphyxia! spasms. Remembering these experimental facts, it is possible to 

 conceive that the heart of Colonel Townsend continued to beat imperceptibly 

 for some time after the cessation of respiration, and that at the end of that 

 time the respiratory centre discharged a group of respirations, which re-estab- 

 lished the circulation. The man, in fact, had sunk into the condition of a 

 hibernating animal, where the metabolic processes are at the lowest ebb. 



It must be borne in mind that the heart, during its systole, by 

 diminishing its own volume, increases the negative pressure in the 

 thorax. In proportion as the ventricles become smaller, the lungs, 

 the thoracic veins and auricles must become larger. On passing a tube 

 down the jugular vein of a horse or dog, there can be observed, besides 

 the respiratory oscillations, short undulations, synchronous with the 

 heart-beat. The fall of pressure in these is synchronous with the 

 systole. 1 On removing the front of the chest wall from a rabbit, with- 

 out injury to the pleura, a to-and-fro movement of the lung can be seen 

 to take place synchronously, with the heat of the heart. Similarly, the 

 chest wall sinks in, outside the area of the cardiac impulse during systole, 2 

 and if the breath be held, a negative pressure appears at the same time 

 in the air passages. This last phenomenon can be recorded 3 by means 

 of a tube placed in one nostril, while the mouth and the other nostril 

 are held closed. The tube is connected with a delicate tambour. The 

 larynx must be kept open during the observation. 



FIG. 31. A, Pressure in the air passage ; B, carotid pulse. Mosso. 



In Fig. 31, a curve of the carotid pulse is simultaneously shown 

 with that of the pressure in the air passages. During the rise of 

 the former, the latter is seen to fall. The fall is found to begin earlier 

 than the rise of the carotid pulse, because it is dependent 011 two 

 factors. The first of these is the contraction of the ventricle, which drives 

 outwards the wall of the thorax ; the second factor is the expulsion 

 of the blood from the thoracic cavity. The first factor produces its 

 effect on the nasal tracing earlier than the second, while the rise of 

 pressure in the carotid artery is produced only by the latter. Part of 

 the difference in time is due to the fact that the rate of transmission in 

 the air-tubes is far greater than that" of the pulse wave along the 

 arteries. If, in the course of this experiment, the larynx be closed, 

 the pressure is found to rise in the nose with each systole, owing to the 

 expansion of the arteries in the mouth, nose, and pharynx. 



1 Wedemeyer, " Untersuch. ueber d. Kreislauf des Blutes," Hanover, 1828; Weyrich, 

 " De cordis aspiratione," Dorpat, 1853. 



2 Loven, Nord. med. Ark., Stockholm, 1870, No. 19, vol. ii. 



3 Mosso, "Die Diagnostik des Pulses," Leipzig, 1879, S. 42. 



